There is currently a fleet in excess of one million rail cars operating in the United States. Keeping track of the movement of each of these rail cars as they are interchanged between railroads is a daunting task, yet one which must be accomplished accurately and economically to maintain competitiveness with other transportation methods. Accordingly, the Association of American Railroads has adopted an Automatic Equipment Identification (AEI) program. Under this program, two transponders will be attached to each rail car, one on each side of the car. Each transponder has a unique code stored within its memory which identifies the individual rail car. Readers will be dispersed throughout the track system in the United States to read the transponders. The data from the readers will be fed into a central processing unit so that information on the location and direction of travel of each car can be continuously and automatically updated.
In view of the large number of rail cars which must be "tagged" with transponders, it is vital to the success of this program that a reliable, inexpensive and labor saving method be developed for attaching the transponders to the rail cars. In the past, glue or double sided adhesive tape has been used to attach the transponders. However, the long term durability of such attachments is questionable. In addition, transponders have been attached directly to the sides of rail cars by screws and pop rivets. However, this approach is labor intensive and is impractical with tank cars.
More recently, it has been proposed to attach the each transponder to its rail car via a bracket welded to the side of the rail car. Under this approach, a primary bracket having inward facing edges around its periphery is placed against the side of the rail car so that only the edges contact the car. The primary bracket is then welded along its sides to the rail car. In order to attach the transponder to the primary bracket, each of the transverse ends of the transponder are slipped under fingers extending from the face of the primary bracket and two screws are threaded into the primary bracket, one screw extending through each of two holes located in flanges formed at each end of the transponder. A secondary bracket is then installed adjacent one longitudinally extending side of the transponder and the secondary bracket is attached to the primary bracket by two additional screws.
Unfortunately, the attachment system described above suffers from several serious disadvantages that could jeopardize the successful implementation of the AEI program. First, since the bracket contacts the rail car along only the inward facing edge of the primary bracket, there is a poor conduction heat transfer path between the transponder and the rail car. As a result, when the rail car is cycled through a thawing shed, in which the car and its contents are briefly heated--for example, by infra red lamps--to allow bulk material to be unloaded during sub-freezing weather, the transponder can become overheated and damaged because of the inability to rapidly transfer large quantities of heat to the large thermal mass of the rail car. Second, the installation of the transponder and bracket is labor intensive, involving the installation of four screws and two bracket components. This is a significant drawback since successful implementation of the AEI program will require installing over two million transponders. Third, since the primary bracket blocks access to the transponder memory port, the transponder must be programmed with its unique identification code prior to its assembly to the bracket. This situation precludes assembling the transponder and bracket in the factory and storing them as a unit until the transponder is ready to be programmed and matched with a rail car. Fourth, if the screws attaching the transponder to the bracket are over torqued, the plastic transponder attachment flanges can be cracked, thereby requiring replacement of the transponder. Since two transponders are required for each rail car, breakage of one transponder requires reprogramming another transponder with the appropriate individual identification code of the rail car.
Accordingly, it would be desirable to provide a system for automatic identification of rail cars which featured a method of attaching a transponder to a rail car which was labor saving, provided good heat conduction to the rail car, precluded over torquing of the attaching means, and allowed programming the transponder memory after assembly of the transponder to its attachment bracket.